1. Field of the Invention
The invention relates to the manufacture of pocketed springs for mattresses, and for cushions for upholstered furniture.
2. Background and Description of Related Art
Pocketed springs are typically produced in strips of springs individually encased in pockets formed by seaming a strip of textile fabric folded upon itself longitudinally. Strips of such springs are then assembled side-by-side with the axes of the springs parallel, and joined by various techniques to produce a pocketed spring core for a mattress or cushion.
Such assemblies, long known to the trade, are referred to as Marshall units or "constructions", after the man thought to have originated the pocketed spring. See U.S. Pat. No. 685,160 of 1901. The best known example in the U.S. and Canadian markets of mattresses employing pocketed spring constructions is the Beautyrest mattress of Simmons Company, which was responsible also for much of the development of machinery for the automated production of pocketed springs. Significant representative patents are those of Simmons' early machine designer, John F. Gail, e.g., U.S. Pat. Nos. 1,685,566, 1,733,660, and 1,813,993.
The pocket fabric then used was woven cotton sheeting, in which the longitudinal and transverse seams which defined the pockets were lines of stitching performed by sewing machines. As ultimately developed, the compressed springs were inserted seriatim between the plies of the folded strip and maintained in the compressed condition by appropriate external constraint upon the moving strip. Sewing machines then sewed across the strip between the compressed springs to define the individual pockets about the springs, and longitudinally at the overlapped edges of the strip to close the pockets and confine the springs therein when the external restraint was subsequently released.
Upon the release of restraint, each spring expanded in the position in which it was inserted, i.e., with its ends pressing against the side walls of the pocket. Unstable in this position, the occasional spring would right itself in its pocket, but most would not, until manipulated externally to turn the spring in the pocket, allowing it to expand to the maximum height, transversely of the strip, permitted by the restraining pocket.
The further developments of the Gail technique in more recent times have been those related to the introduction of non-woven fabrics of thermoplastic fiber, and the substitution of thermal welding of such fabrics for sewing, as in U.S. Pat. No. 4,439,977. Those changes, in turn, and others as well, have ushered in a very substantial reduction in size and complication of the pocketed-spring-making apparatus, thereby removing a great deal of cost of the apparatus while improving its reliability and rate of production.
Basically, however, the Gail process, as described, has, until the present invention, undergone only minor change. The compressed spring is inserted between the sheets, a pocket is defined around it, the compression of the spring is released, and the spring is manipulated within the pocket to enable it to reach its maximum extension permitted by the pocket, i.e., with the spring axis oriented transversely of the strip.
This process, proven by time and used throughout the industrial world, is, however, not without its limitations. For example, it is difficult to adjust the apparatus to vary the spacing of the cross seams of the strip to accommodate springs of different diameter, or to alter the frictional grip of the pocket material upon the spring for its effect in varying the spring constant of the combination. Moreover, when making pocketed springs of reduced height relative to spring diameter, as for seat cushions, for example, it is often difficult to turn the spring within the completed pocket to align the spring axis transversely of the strip.
The departure of the improved and simplified method of this invention from the traditional method, and the apparatus herein disclosed for carrying out the improved method of the invention, not only overcome the stated limitations of the traditional method, they also result in a basic change in the pocketed springs from those produced by the traditional method, a change of product which the trade hailed as improvement but never accomplished satisfactorily on a production basis.